Its "extremely dangerous core" is forecast by the US National Hurricane Center to move over parts of the northern Virgin Islands on Wednesday, passing near or just north of Puerto Rico, then passing near or just north of the coast of the Dominican Republic on Thursday.

Thousands of people have been evacuated from at-risk areas across the Caribbean. Residents have flocked to shops for food, water, and emergency supplies, and airports have closed on several islands which are popular holiday destinations.

In the US, Florida's Key West area has ordered a mandatory evacuation, with landfall expected at the weekend.

Officials in the nearby French territory of Guadeloupe confirmed that on St Barts, the fire brigade station had been flooded with a metre of water, there is a total power blackout and many roofs have been blown off. On Saint Martin, the prefecture building was severely damaged, the fire station was out of order, there was a power blackout and several roofs at the police station were torn off.

Ms Girardin said the hurricane had caused major flooding in low-lying areas, and coastlines were being "battered extremely violently" by the sea.

Some 40,000 people live in the French part of Saint Martin, with around the same number estimated to live on the Dutch side. About 9000 people live on St Barts.

Search and rescue crew members clear a fallen tree during a search mission as hurricane Irma hits Puerto Rico in Fajardo. Photo: AFP

In the Dutch territory, known as Sint Maarten, the airport has been closed with photos showing debris strewn across the departures area and outside.

There has been a total power blackout, streets are littered with debris, cars are underwater and boats in the ports have been destroyed, Dutch broadcaster NOS reports (in Dutch).

France's interior minister said three emergency teams were being sent to the islands, two from France and one from Guadeloupe.

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